In the semiconductor field it is common to sequentially perform various steps in the fabrication of a semiconductor device. The steps can include growing several different layers of semiconductor material and the use of various masks and etching steps to form the desired devices and terminals on the devices. In some methods, masking material, e.g. nitride/oxide or the like, is applied and semiconductor material is grown over masked and unmasked areas. The material on the masked areas is then removed by etching and lift-off. In some instances material is selectively grown in unmasked areas and the masking material is then removed. In some processes a photoresist mask is used to define and develop a hard mask, i.e. a metal mask, a nitride mask, etc.
Generally, in these prior art methods of fabricating semiconductor devices, etching is required to remove unwanted material and masks are removed by etching, solvent, or the like. During the etching and/or mask removal processes, the material of the semiconductor device has a high likelihood of being contaminated by the etchant, which contamination greatly reduces the life of the device, the operating characteristics of the device, and the reliability of the device. Further, the etching process severely damages semiconductor material adjacent the etched areas which further reduces life, operating characteristics, and reliability. Also, etching processes are very time consuming and difficult to perform.
Thus, these prior art techniques involve many process steps such as resist spinning, exposure, developing, cleaning and so on. All of these processes can introduce contamination, decrease yield, etc. A further problem that arises is that the structure or substrate (generally a wafer) must be removed from the growth chamber to remove the masking material. The structure is then masked again and re-introduced into the growth chamber for re-growth. Thus, the prior art techniques keep the wafer vacuum incompatible.
In addition to the masking and etching problems, all known prior art fabrication processes require many interspersed growing, masking and etching steps which greatly complicate and lengthen the process. For example, when epitaxial layers are grown, the wafers must be placed in a vacuum or pressure chamber to provide the atmosphere for the growth. Each time the wafer must be etched and/or masked, it must be removed from the chamber, resulting in large amounts of preparation time for each step. Also, each time wafers are removed from a chamber and subsequently replaced, the opening and preparation of the chamber (as well as the processing of the wafer) is an opportunity for additional impurities and contaminants to be introduced to the wafer.
Many of these problems have been overcome by the use of resistless patterning. However, in the resistless patterning approach the oxide mask formed is very thin. This thin oxide mask cannot serve as an implantation mask in normal processing.
Accordingly, it would be highly desirable to provide a new and improved resistless process for implantation.
It is a purpose of the present invention to provide a new and improved method of implantation having reduced steps.
It is another purpose of the present invention to provide a new and improved method of implantation which is vacuum compatible.
It is still another purpose of the present invention to provide a new and improved method of implantation which does not require the introduction of contaminants, such as photoresist, solvents and etchants.
It is a further purpose of the present invention to provide a new and improved method of implantation which is much simpler and includes less chance of contamination of the devices.
And a further purpose of the present invention is to provide a new and improved method of implantation which can be a completely dry process.